LAX01FA252 · Sikorsky S-76A

The pilot got out of the helicopter with the engines running and the rotors turning to check on the security of a cabin door, and the unmanned helicopter began moving on the helipad and rolled over. The pilot had completed a nightime, helicopter, air taxi flight, and was preparing to depart the elevated helipad to reposition the helicopter to the operator's base. After deplaning his passengers the pilot returned to the cockpit and was preparing to depart when he noticed a door unsecured indication on the instrument panel for the left cabin door. The passengers had deplaned through the right-hand door and the left door annunciation had not been on during the inbound flight. He thought one of the passengers might have released the left door latch inadvertently while preparing to deplane. He idled the engines and exited the cockpit to check the door. He reclosed the door and returned to the cockpit; however, the door open annunciation came on again. He recalled leaving the cockpit "2 or 3 times" to deal with the door and said he was "frustrated with it." He did not recall retarding the engine power control levers to ground idle before leaving the cockpit the final time. While out of the cockpit, the wheel-equipped helicopter started to move as the pilot was returning to the cockpit. He recalled it was moving toward the edge of the helipad. He returned to the cockpit; however, before he could regain control there was a confusing sequence of events and the next thing he knew the helicopter was on its side. The pilot reported there were no mechanical discrepancies with the helicopter up to the time of the event. He remarked that it was very light [weight] with no one else on board. On the deck of the helipad there was a tire skid pattern consistent with a dynamic rollover event. The engine power control levers were found in the "fly" position.

Verbatim NTSB analysis and probable cause from the NTSB dataset